Effects of guanabenz and guanfacine on postsynaptic α2-adrenoceptors in the rat submaxillary and parotid glands

Summary The effects of two ₂-agonists (guanfacine and guanabenz) on both the submaxillary and parotid gland of the rat were studied. Whereas guanfacine in doses ranging between 1,000 and 30,000 g/kg i.v. produced an immediate and persistent secretion of saliva from the submaxillary gland, guanabenz in doses as high as 40,000 g/kg did not induce measurable secretion either from the parotid or the submaxillary gland. Secretion clicited by guanfacine was not modified by yohimbine (300 g/kg) but was abolished by prazosin (100 g/kg).In both glands, low doses of either guanabenz (10 g/kg) or guanfacine (100 g/kg) markedly inhibited the secretory responses induced by noradrenaline, methacholine and substance P, but not that induced by isoprenaline. The inhibition caused by the ₂-agonists was greater for noradrenaline than for either methacholine or substance P. Blockade of ₂-adrenoceptors with yohimbine (300 g/kg) did not modify the response to noradrenaline, methacholine or substance P in either gland. However, the same dose of yohimbine injected 5 min before the ₂-agonists prevented the inhibitory effects of guanfacine and guanabenz on the response induced by either one of the three sialagogic agents. Guanabenz (10 g/kg) did not modify the increase in mean blood pressure observed after the different doses of noradrenaline employed to induce salivary secretion. Guanabenz (10 g/kg) and guanfacine (100 g/kg) did not change the time course of the secretion elicited by either noradrenaline, methacholine or substance P, since the degree of inhibition was of similar magnitude at all the periods of time analyzed.The results obtained give further support to the hypothesis that activation of ₂-adrenoceptors in the submaxillary as well as parotid gland of the rat inhibits secretory responses which are mediated by either muscarine, substance P and ₁-receptors and not those elicited by -adrenoceptors.Partially supported by grants no. 3111 k/83 CONICET and Res 40-5/4/84 SUBCYT     

Cholinergic control of gastric acid secretion

Summary In the perfused stomach preparation of the anaesthetized rat the cholinergic agonists acetylcholine (ACh) and bethanechol stimulated gastric acid secretion. Both agonists produced similar maximal acid output (70 mol/15 min) when infused intravenously. However, bethanechol was more potent, eliciting half maximal stimulation at 1.98 mol/kg/h. Secretory responses to either agonist were antagonized in a dose related fashion by blockade of muscarinic receptors with atropine. In contrast, inhibition of nicotinic receptors with hexamethonium produced a striking potentiation of ACh stimulated secretion whilst the bethanechol elicited secretion remained unaffected. In the presence of full nicotinic receptor blockade the ACh response curve was shifted to the left sixfold, half maximal stimulation being produced at 1.79 mol/kg/h. Cimetidine partially inhibited the secretory responses elicited by either ACh or bethanechol while blockade of adrenoceptors ( and ) did not affect acid output induced by cholinergic agonists. Secretion elicited by ACh is interpreted as being the composite effect of prosecretory action and an inhibitory mechanism due to the activation of nicotinic receptors. Hexamethonium, through nicotinic receptor blockade, inhibits the restricting mechanism and thus reveals the full stimulatory action of ACh.     

庆大霉素分泌过程的初步研究

应用恒温系统及缓冲液体系,考察了温度及pH值分泌过程的影响,然后在此基础上又讨论了添加葡萄糖、金属离子Fe^2 、K^ 和Mn^2 以及超声波和微波处理的效果,实验发现,pH＝7．4,温度34℃,以及添加5g／LKCl或50mg／LMnSO4都能刺激庆大霉素的分泌。     

Difenoxin and loperamide: studies on possible mechanisms of intestinal antisecretory action

Summary Experiments have been performed to determine whether the antisecretory (antidiarrhoeal) actions of difenoxin and loperamide are mediated by enteric neurones. An iso-osmotic perfusion solution was circulated around the lumen of the jejunum of anaesthetised rats. Vasoactive intestinal peptide was infused intra-arterially to induce net fluid secretion which was inhibited by difenoxin (ED₅₀, 0.23 mg/kg) and loperamide (ED₅₀, 0.5 mg/kg). However, neither were able to restore the fluid transport rate to the control level of absorption.The antisecretory effects of difenoxin (0.77 mg/kg) and loperamide (0.6 mg/kg) were blocked by the opiate receptor antagonist naloxone (2 mg/kg). Their effects were also abolished by pretreatment with the 5-HT synthesis inhibitor p-chlorophenylalanine (PCPA; 200 mg/kg; with desmethylimipramine given beforehand to protect noradrenergic nerves and enhance 5-HT depletion). The effect of difenoxin was blocked with methiothepin (1 mg/kg) and methysergide (30 g/kg) but not ketanserin (30 g/kg), ritanserin (30 mg/kg), ondansetron (10 g/kg) or ICS 205-930 (3 mg/kg). None of the above 5-HT receptor antagonists modified the antisecretory effect of loperamide. The antisecretory effect of difenoxin but not loperamide was prevented by phentolamine (2 mg/kg) and by pretreatment with 6-hydroxydopamine (150 mg/kg) total.It is concluded that both difenoxin and loperamide inhibit net fluid secretion by indirect mechanisms. It is proposed that the initial action is on enteric -opiate receptors and that this results in the release of 5-HT. In the case of difenoxin, the 5-HT may act on 5-HT₁-like receptors to release noradrenaline. However, the major difference in the mechanism of action of loperamide compared to difenoxin is that it does not utilize noradrenaline as the final mediator of its antisecretory action.Correspondence to A. De Luca at the above address     

Decrease of Interleukin-2 secretion is a new independent prognostic factor associated with poor survival in patients with small-cell lung cancer

Background: We have previously shown that suppression of Interleukin-2(IL-2) secretion was mediated by transforming growth factor (TGF) 1secreted by small-cell lung cancer (SCLC) tumor cells. We have also shown thatIL-2 secretion was significantly impaired in patients with SCLC at the timeof diagnosis. Reconstitution of cytokine secretion correlated with reductionof tumor load. These data suggested that the immune system was suppressed bythe tumor. To address the clinical relevance of cytokine suppression in SCLC,we investigated the correlation of the level of IL-2 secretion with survival.Patients and methods: The significance of correlations between singleparameters in the test groups was calculated by using the linear regressionanalysis, the Wilcoxon rank sum test and the exact test according to Fisher.Using the Kaplan–Meier method, the log-rank test and the Cox-regressionmodel, we analysed the relation of IL-2 secretion in whole blood cell culturesfrom 52 patients with SCLC at the time of diagnosis to established prognosticfactors relevant for survival in SCLC.Results: Impairment of IL-2 secretion significantly correlates to survivalin SCLC (P = 0.004). Further univariate and multivariate analysis showed thatthis prognostic factor is independent from other factors of prognosticrelevance in SCLC, namely stage of disease, neurone specific enolase (NSE),lactate dehydrogenase (LDH), age, and sex. More important, the prognosticvalue of IL-2 secretion is comparable to the most predominant prognosticfactors for survival in SCLC identified so far. In the final model of the coxregression analysis, the P-value for IL-2 secretion in relation to stage ofdisease was 0.012 and 0.019, respectively.Conclusions: IL-2 secretion at the time of diagnosis represents anindependent prognostic factor for survival in SCLC. Although its prognosticvalue has to be confirmed in a larger group of patients, our resultsdemonstrate that IL-2 secretion may play an important role in diagnosis andtreatment of SCLC. Moreover, in contrast to other prognostic factors,impairment of IL-2 secretion may help to understand immunosuppression in SCLCand, thus, important elements of the pathogenesis of this disease.     

Effect of platelet-activating factor on secretion of mucous glycoprotein from chinchilla middle ear epithelial cells in vitro

Platelet-activating factor (PAF) is a naturally occurring phospholipid that acts as a pleiotropic mediator and mediates cell-cell reactions under physiological and pathological conditions. Recently, it has been shown that PAF is a strong secretagogue of mucous glycoprotein in the airways, suggesting its role in mucous glycoprotein secretion and the pathogenesis of otitis media with effusion. In the current study, we examined the effect of PAF on mucous glycoprotein secretion in cultured chinchilla middle ear epithelial cells. PAF at 1 M significantly stimulated mucous glycoprotein secretion from cultured chinchilla middle ear epithelial cells. This action was concentration-dependent, with secretions reaching near maximum when the cells were incubated with PAF at 100 M. In a time-dependent study, PAF demonstrated an initial rapid stimulation of mucous glycoprotein secretion, followed by a gradual increase thereafter. A six-fold increase was seen in the first 2 h compared with controls. Cycloheximide, a protein synthesis inhibitor, demonstrated an inhibitory effect on PAF-stimulated mucous glycoprotein secretion in this study. These findings suggest that PAF plays an important role in the pathogenesis of otitis media with effusion by stimulating mucous glycoprotein secretion in vitro.Supported by NIH grant P0I-D000133 from the National Institute on Deafness and Other Communication Disorders.     

Eicosanoid-mediated Cl− secretion induced by the antitumor drug,irinotecan (CPT-11), in the rat colon

Irinotecan (CPT-11) is active against a broad range of human cancer. One of the side-effects of irinotecan is a strong diarrhoea. In order to investigate the mechanism underlying this diarrhoea, the effect of irinotecan on anion secretion across the isolated rat distal colon was studied. Irinotecan caused a concentration-dependent increase in short-circuit current (Isc). The increase in Isc was completely dependent on the presence of Cl^– ions and was supressed by furosemide and the Cl^– channel blocker NPPB (5-nitro-2-(3-phenylpropylamino)-benzoate), indicating that it is caused by a Cl^– secretion. The secretory response was inhibited by indomethacin, 1-benzylimidazole, a thromboxane synthase inhibitor, and SK&F 88046 ((N,Nbis-[7-(3-Chlorobenzeneaminosulfonyl)-1,2,3,4-tetrahydroisoquinolyl)disulfonylimide), a thromboxane A₂ receptor blocker. In isolated crypts irinotecan had no effect on the membrane potential. Consequently, the secretion induced by irinotecan is an indirect one, caused by the stimulation of eicosanoid production, e.g. thromboxane A₂, in the subepithelial tissue.     

Ultrastructural neuropathologic effects of Taxol on neurons of the freshwater snailLymnaea stagnalis

Summary Cerebral ganglia of the freshwater snailLymnaea stagnalis were incubatedin vitro in 10 M Taxol for 8 and 24 h. Cremophor EL (0.1%) was used as a diluant. The tissue was processed for electron microscopy. Various ultrastructural parameters were assessed quantitatively. Cremophor EL appeared to seriously affect the cell somata of the multipeptidergic caudodorsal cells. In the Cremophor-controls the mean area of Golgi zones, the percentage dense material (neuropeptides) in these zones, the number of large electron dense granules (these are involved in neuropeptide processing) and the mean nuclear heterochromatin clump size, were significantly smaller than in the Ringer-controls, whereas the number of lipid droplets was higher. All these parameters, except for the lipid droplets, were not different in the Cremophor-controls and the Taxol-treated specimens. After 24 h treatment, but not after 8 h, Cremophor EL furthermore induced an increase in the number of axonal microtubules. It is argued that the results might signify activation of the neurons by Cremophor EL. Taxol induced a significant increase in the number of microtubules in axons and cell somata. Furthermore an increase in the number of Golgi zones was observed, suggesting activated neuropeptide synthesis. In all groups immunostaining with antibodies to neuropeptides produced by the caudodorsal cells was normal. Release of neuropeptide (exocytosis) from axon endings was elevated after Taxol treatment, and exceptionally high in specimens cotreated with Taxol and Org 2766 (incubation time 22 h). The effect of Org 2766 and Taxol on the number of microtubules was cumulative. It is argued that transport of neuropeptide granules from the cell somata to the axon terminals was not affected by Taxol. It is concluded that Taxol neurotoxicity is probably not due to impeded microtubular axonal transport.     

Growth hormone secretion in children and adolescents with familial tall stature

Sixty-five patients (22 boys and 43 girls) presenting with familial tall stature were investigated with regard to growth hormone (GH) secretion, both physiological and after stimulation with thyrotropin releasing hormone (TRH) and growth hormone relasing hormone (GHRH). Plasma insulin-like growth factor-I (IGF-I) was also measured. Two groups of patients were distinguished according to their physiological secretion of GH: a high secretory group (n=49) with a mean 24 h integrated concentration of GH (IC-GH) of 5.4±2.3 g/l per minute and a large number of peaks (5.1±1.6 in 24 h), and a low secretory group (n=16) with a mean 24 h IC-GH of 2.1±0.5 g/l per minute and few peaks (3.3±1.3 in 24h). Plasma IGF-I levels and GH peak values after the TRH test were significantly higher in the high secretory group. These results indicate that familial tall stature is the consequence either of hypersecretion of GH or of hypersensivity to this hormone (IGF-I levels being normal in spite of low GH levels).     

Microelectrode measurements of the effects of basolateral adenosine in polarized human intestinal epithelial cells in culture

 Activation of the basolateral receptor for adenosine in HT-29cl.19A cells, by 100 μM adenosine, increased the equivalent short-circuit current (ΔI _sc= 24±2 μA/cm²), depolarized the intracellular potential (ΔV _a= 26±2 mV) and decreased the fractional apical membrane resistance (ΔfR _a=–0.48). The changes in all parameters reached their peak values simultaneously. This suggests that the primary action of the adenosine-activated pathway is on only one membrane. Bumetanide inhibited the transepithelial response and repolarized the cell potential. After preincubation with 100 μM forskolin, application of 300 μM adenosine caused a significant further change in V _a, I _sc, the transepithelial potential (V _t) and fR _a. Together with the results from ion-replacement studies, the observations indicate that adenosine activates channels other than the cystic fibrosis transmembrane conductance regulator (CFTR). The rank order of potencies of adenosine and adenosine analogues implies that the receptor is of the A₂ subtype. Preincubation with 4-bromophenacyl bromide (4-BPB) inhibited the effect of an adenosine analogue by 50%, indicating that activation of phospholipase A₂ may be involved in the adenosine-induced response. Received: 5 August 1998 / Received after revision: 12 October 1998 / Accepted: 5 November 1998